Elevator systems exist that, in the event of a power system failure, move an elevator car or allow the elevator car to be moved to the next lower floor. A backup power supply system often moves the elevator car to the next lower floor very slowly, or gravity is used to allow the elevator car to move down to the next floor. When the elevator car arrives at the next lower floor the elevator car doors are then opened using the backup power supply system, or the doors may be pried open.
A problem with conventional battery backup systems is that the battery loses power overtime and may not have enough power to move the elevator car to a floor and open the door to allow the passengers to get off of the elevator car safely. As such, the battery must be routinely checked to ensure sufficient battery power, and replaced in the event there is insufficient power. Since batteries may discharge at different rates depending on factors including heat, age, and usage, determining the frequency of battery checks is difficult.
Another problem with conventional elevator backup systems is that due to the size requirements, and resultant weight of the battery or generator which is to provide the necessary power to backup the elevator system, the backup battery or generator must be kept separate from the elevator, and in particular at the bottom of the elevator shaft, for example, in the basement of the building housing the elevator. However, severe storms, for example, hurricanes, that can cause elevator power system failures, may be accompanied by heavy rain that may result in building flooding, which would render the battery backup or generator stored in the basement of the building unusable. Further, a flooded area containing a submerged or partially submerged backup battery or generator may result in dangerous conditions, as chemicals within the battery or generator may leach or leak out into the floodwater.
What is needed are new elevator backup systems, for example, in the form of a rechargeable battery, that avoid the problems outlined above. An elevator backup system in the form of a rechargeable battery that avoids the problems outlined above must overcome problems of conventional rechargeable batteries, which move current from an active material to an external terminal through effectively parallel paths. In general, current is collected from one side of an electrode, often through a single tab. Thus, a current restriction is created at the tab connection where the current paths merge. The created current restriction creates resistance that increases with the size of the electrode. Thus, there exists a minimum limitation on the size of batteries for a given performance (power, efficiency, etc.).
While ZnMn chemistries for batteries are low cost and lightweight, are environmentally benign, and have a very long charge retention, currently, the only batteries (rechargeable or non-rechargeable) commercially available with ZnMn chemistries are round bobbin cells. Round bobbin cells have a positive electrode that is stamped or pressed into a cylindrical hollow pellet and seated into a can, and the negative electrode is a gel that is filled into the center void of the positive electrode.
The high internal resistance of low capacity round bobbin cells limits the currents (i.e., power) that they can deliver. In contrast, flat plate (electrode) cells can be scaled up to large sizes providing high currents and storage capacities.
CA 2 389 907 A1 relates to a method of producing flat plate electrodes in a small format that exhibit high current densities, higher utilization of the active materials, and better rechargeability. The method of forming the electrodes requires the active materials, binders, thickening agents, additives, and an alkaline electrolyte to form a paste that is applied to a current collector. CA 2 389 907 A1 provides is a flat plate rechargeable alkaline manganese dioxide-zinc cell.
An elevator backup system in the form of a rechargeable battery that avoids the problems outlined above should exhibit improvements in, for example, current density, memory effect (i.e., capacity fade), shelf life, charge retention (e.g., at higher operation temperatures), and voltage level of discharge curve over known round bobbin and flat plate cells.